This invention is generally directed to processes for the preparation of chalocogens, and chalcogenide alloys, and more specifically the present invention is directed to the preparation of non-crystalline chalcogenides, and chalcogenide alloys, or of chalcogenides, and chalcogenide alloys of a specific average crystallite size, (ACS). In one embodiment of the present invention there is provided a process for the preparation of small particles of selenium, selenium alloys, trigonal selenium, trigonal tellurium, and trigonal selenium tellurium alloys by the reduction reaction, or coreduction reaction of the corresponding chalcogen, or chalcogenide esters. Accordingly, there is provided in accordance with the present invention a simple, economically attractive, low temperature process for the direct preparation of small particle chalcogens, and chalcogenide alloys of desired average crystallite size, or of a non-crystalline nature by controlling the temperature of the ester reduction reactions involved. The resulting chalcogens, and chalcogenide alloys are useful for the preparation of xerographic photoconductive compositions, which can be incorporated into electrostatic imaging systems.
The incorporation of selenium or selenium alloys into xerographic imaging members is well known. These members can be subjected to a uniform electrostatic charge for the purpose of sensitizing the surface of the photoconductive layer, followed by exposure of an image to activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating member, wherein a latent electrostatic image is formed in the non-illuminated areas. The resulting image may then be developed and rendered visible by depositing thereon toner particles containing resin components and pigment components.
Recently, there have been developed layered organic and inorganic photoresponsive devices containing amorphous selenium, trigonal selenium, amorphous selenium alloys, or halogen doped selenium alloys. One such photoresponsive member is comprised of a substrate, a photogenerating layer containing metal phthalocyanines, metal free phthalocyanines, vanadyl phthalocyanines, or selenium tellurium alloys, and a diamine transport layer reference U.S. Pat. No. 4,265,990.
Many processes are known for the preparation of chalcogenide alloys, particularly selenium containing alloys useful as photogenerating substances, including, for example, melt blending of the elemental substances such as selenium and arsenic in the proportions desired in the final alloy product. Thus, for example, there is disclosed in U.S. Pat. No. 3,634,134 the preparation of arsenic-selenium alloys by melt blending of the appropriate proportions of arsenic and selenium. A similar melt blending method for preparing selenium alloys is disclosed in U.S. Pat. No. 3,911,091.
Also there is disclosed in U.S. Pat. No. 4,007,255 a process for preparing stable red amorphous selenium containing thallium by precipitating selenious acid, containing from about 10 parts per million to about 10,000 parts per million of thallium dioxide, with hydrazine from a solution thereof in methanol or ethanol containing not more than about 50 percent by weight of water, at a temperature between about -20 degrees Centigrade and the freezing point of the solution, wherein the resulting precipitate is maintained at a temperature of from about -13 degrees Centigrade to about -3 degrees Centigrade.
Disclosed in U.S. Pat. No. 3,723,105 is a process for preparing a selenium tellurium alloy by heating a mixture of selenium and tellurium containing 1 to 25 percent by weight of tellurium to a temperature not lower than 350 degrees Centigrade to melt the mixture, followed by gradually cooling the molten selenium and tellurium to around the melting point of the selenium tellurium alloy at a rate not higher than 100 degrees Centigrade per hour, and subsequently quenching to room temperature within 10 minutes.
Other processes for the preparation of selenium, or selenium alloys are disclosed in U.S. Pat. Nos. 4,121,981 and 3,524,745.
There is also described in copending applications the preparation of selenium in high purity, by the reduction of selenium esters, subsequent to purification, with for example hydrazine; and the preparation of chalocogenide alloys of high purity by the simultaneous low temperature coreduction of the appropriate purified chalcogenide esters. Further there is disclosed in U.S. Pat. No. 4,432,841 the preparation of selenium alloys by the electrochemical coreduction of the corresponding pure esters. While these processes are suitable for their intended purposes there remains a need for improved processes for the preparation of chalocogens, and chalcogenide alloys. Also there remains a need for improved processes for the preparation of chalcogens, and chalocogenide alloys wherein products can be obtained of certain average crystallite sizes. Additionally there continues to be a need for processes for the preparation of chalocogens, and chalocogenide alloys wherein the average crystallite sizes of the products resulting are directly dependent on the temperature of the reduction reaction. Moreover, there continues to be a need for an improved simple economically attractive, direct process for the preparation of noncrystalline chalcogenide alloys of high purity. Also, there is a need for improved processes wherein chalcogenide binary and ternary alloys can be obtained in high purity by utilizing substantially similar process parameters and apparatus. Further there continues to be a need for improved processes for the preparation of high purity chalcogens and chalocogenide alloys, wherein solvents selected for the preparation can be recycled. Also, there continues to be a need for improved processes for preparing chalcogenide alloys, and chalocogens that are homogeneous, are of a crystalline form, can be obtained in various proportions without using high temperature reaction conditions, and are of certain average crystallite sizes.
These needs can be satisfied in accordance with the process of the present invention wherein chalocogens, and homogeneous chalcogenide crystalline alloys of a desired average crystallite size are obtained, by the reduction of pure esters, or by the coreduction of a mixture of chalcogenide esters, rather than a mixture of the starting elemental components. In those situations where the rates of reductions of the esters are comparable, a composition of the resulting alloy mirrors is substantially identical to the molar composition of the mixture of esters. In other situations, when the reduction rates are not comparable, the composition of the alloys, especially with regard to ternay alloys, may not mirror the molar composition of the elements contained in the mixture of esters. Also there remains a need for processes for the preparation of noncrystalline chalcogens, and their alloys, and small particle chalcogens and their alloys of desired average crystallite sizes, wherein the resulting particles are easily dispersable in a polymer solvent system.